In general, in order to manufacture semiconductor integrated circuits such as integrated circuits (ICs), large scale integrated circuits (LSIs), substrates such as semiconductor wafers are subjected to heat treatments such as film forming treatment, oxidizing and diffusing treatment, etching treatment, annealing treatment. In the related art, a vertical batch type heat treatment apparatus is used to treat a plurality of substrates at once.
In such heat treatment apparatus, a wafer boat loading a plurality of (for example 100 to 150) substrates such as semiconductor wafers is ascended and loaded (or inserted) into a vertical processing container made of quartz from a loading chamber having an inert gas atmosphere which is located below the processing container, and heat treatments such as film forming treatment are performed in the sealed processing container. After the heat treatments are performed, the wafer boat is unloaded (or descended) to replace the treated substrates with untreated wafers. Then the same heat treatments as described above are repeated.
A boat elevator installed within the loading chamber is used to elevate the wafer boat and moving and loading of the substrates are performed by a moving and loading mechanism installed within the loading chamber.
However, as described above, for the purpose of preventing natural oxidation of the semiconductor wafers such as silicon substrates and cooling the unloaded substrates having a high temperature, inert gas such as nitrogen gas is horizontally flown into the loading chamber installed below the processing container having a high temperature to bring the loading chamber into an inert gas atmosphere. The nitrogen gas is circulated and reused. In addition, the nitrogen gas is properly supplemented such that an oxygen concentration in the internal atmosphere of the loading chamber is lower than a predetermined value.
However, a large quantity of nitrogen gas is needed to put the entire internal atmosphere of the loading chamber having a considerably high capacity under the nitrogen gas atmosphere at all times. Such need of the large quantity of nitrogen gas may result in high running costs. In addition, since the nitrogen gas acting as cooling gas is flown throughout the loading chamber, a stream of gas which has no contribution to cooling the substrates may exist, which make it difficult to achieve an efficient cooling and takes a long time for cooling, which results in a low throughput.
In particular, in recent years, for the purpose of further improving the productivity of semiconductor integrated circuits, a diameter of substrates has been demanded to become larger, for example from 300 mm to 450 mm. To meet such increase in the diameter of the substrate, a pitch of substrates loaded on the wafer boat had to be increased as well to flow sufficient process gas between the substrates. For example, a pitch of substrates having a diameter of 300 mm is 6 to 7 mm, whereas a pitch of substrates having a diameter of 450 mm is required to be 8 to 12 mm.
Even in this case, since the number of substrates to be treated at once is required to be the same as in the conventional batch type heat treatment apparatus, for example, 100 to 150. Due to a high demand for improving the productivity, a height of the processing container, a length of the wafer boat and a stroke to elevate the wafer boat are increased by the amount of increase in the substrate pitch. As a result, there is a strong need to overcome the above problem that a large quantity of nitrogen gas is needed for a higher volume (or capacity) of a processing unit including the processing container and the loading chamber located below the processing unit.